1. Technical Field
The invention relates generally to systems for projecting laser light (or other electromagnetic radiation), and more particularly relates to systems for projecting a sheet of laser light. In even greater particularity, the invention relates to projecting a laser reference plane.
In one aspect of the invention, a laser beam is converted into a radially extending, omnidirectional substantially planar sheet of laser light for use as a reference plane for construction projects.
2. Related Art
Converting a laser beam into an omnidirectional sheet of laser light has a number of useful applications. For example, a substantially planar sheet of laser light can be used as a reference plane or marker, such as in the construction industry.
Without limiting the scope of the invention, this background information is provided in the context of a specific problem to which the invention has application: projecting a laser reference plane with a minimum of moving parts and critical adjustments.
Current techniques for converting a laser beam into a reference plane include:
(a) using a curved lens, (b) using a rotating prism/mirror/laser, and (c) using a stationary reflecting cone.
FIG. 1a, 1b, and 1c illustrate the curved lens approach with three different lens geometries. The laser beam is incident to a cylindrical lens with a typical curvature of about 1 mm radius. The lens projects a fan of laser light (an effect described by geometrical optics). Taboada et.al., Rev. Sci. Instruments (Vol. 44, No. 9. September 1973, p. 1240) describes using a cylindrical lens to generate the reference plane. A disadvantage of the cylindrical lens approach is that the light plane is limited to about 90 degrees of subtense, which has limited utility for many reference plane applications (such as in the construction industry).
FIG. 2 illustrates the rotating prism/mirror approach which is described further in U.S. Pat. Nos. 3,588,249 (Studebaker), 4,062,634 (Rando), and 4,830,489 (Cain). A plane of light is projected radially outward from a prism or mirror which is rotated continuously through 360 degrees to sweep out the given reference plane. A variation of this approach is to use a rotating laser such as described in U.S. Pat. Nos. 5,576,826 and 5,307,368 (Hamar). A number of disadvantages of the rotating prism/mirror/laser approach results from the requirement of rotational mechanical movement, including control for vibration, gyroscopic force, and alignment, as well as precision bearings and special housing.
FIG. 3 illustrates the reflecting cone approach, which is described further in U.S. Pat. 4,111,564 (Trice). A laser beam, preferably one that is in the TEM01 mode which is characterized by a donut shaped transverse light distribution, is incident along the axis of a reflecting cone. The projected light defines a reference plane. Disadvantages of the reflecting cone approach include the requirement of a precisely defined input circular beam (TEM00 or TEM01), and limitations due to relatively stringent alignment demands (even a change of 1 arc second in the incident angle of the laser beam can cause an objectionable change in the light plane to an umbrella-like distribution. These alignment demands are addressed in U.S. Pat. No. 5,335,244 (Dugan), which still requires alignment adjustments and additional optical components to achieve the desired performance.